Techniques are known that detect the position and orientation of a portable terminal device. An example of such techniques uses an electromagnetic wave emitted by a base station. For example, the position is estimated based on the radio field intensity of the electromagnetic wave received by the portable terminal device from a base station, such as an access point of a wireless local area network (LAN) or an ultra-wideband (UWB) base station. Although this technique is suitable for estimating a rough position of the portable terminal device, the accuracy of the technique has its own limitations.
Another example of such techniques uses a marker. In this case, the position and orientation of the marker displayed on a display of the portable terminal device is detected from an image captured by a camera installed on the side of the environment. Using the marker in this manner allows the position and orientation to be detected more accurately than in the case of using the radio field intensity.
Conventional techniques are described, for example, in the following patent documents:
Japanese Laid-open Patent Publication No. 2013-101128; and
Japanese Laid-open Patent Publication No. 2010-20374.
As will be described below, however, the technique described above is difficult to detect a low-resolution marker.
Specifically, the above-mentioned camera on the environment side is not necessarily installed at a location from which the camera can capture the marker at a high resolution. For example, in some cases, the camera is installed at a location, such as on a ceiling, from which the environment can be viewed down so as to expand a range allowing the camera to capture the marker to a larger range. In this case, the camera captures the image from a location relatively far from the marker, so that the marker displayed in the image is smaller, resulting in capturing a low-resolution marker. When the marker is captured at a low resolution in this manner, it is difficult to detect the position and orientation of the marker, and it is difficult to identify identification information indicated at the marker. This problem restricts the location of the camera installed on the environment side, thus impairing the versatility of the marker detection.